This invention relates to a method and device for the decontamination of a media, such as groundwater or groundwater and soil, containing per- and polyfluoroalkyl substances (PFAS) and related compounds such as PFAS precursors, collectively referred to as PFAS contaminants. More specifically, the invention relates to a system and method for concentrating and removing PFAS contaminants from soil and groundwater, preferably using in-situ gas injection and collection of the resulting foam.
PFAS are contained in fire-fighting agents such as aqueous film forming foams (AFFF) and as such have they been used extensively at facilities such as military bases and airports over the past fifty years. They have also been used in the manufacture of many consumer goods for grease repellency and water-proofing. More recently, long-chained PFAS in particular have been shown to bioaccumulate, persist in the environment, and be toxic to laboratory animals, wildlife, and humans. As a result of these observations, on May 19, 2016 EPA established a health advisory for the long-chained PFAS constituents; perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) of 70 parts per trillion in drinking water.
PFAS have unique chemistry. The carbon-fluorine bond is one of the strongest bonds in nature and it is very difficult break. In addition, PFOA and PFOS, for example, have a perfluorinated carbon tail that preferentially partitions out of the aqueous (water) phase and an ionic headgroup that partitions into the aqueous phase. (See FIG. 1.) This causes PFAS to preferentially accumulate at air/water interfaces.
Because of these characteristics, traditional in-situ remediation technologies such as chemical reduction, chemical oxidation, and bioremediation have not been shown to be effective in treating PFAS. Thermal treatment can be effective, however very high temperatures are needed (greater than 1,770 degrees F.) for complete destruction thereby making in-situ treatment either impracticable or very expensive. Groundwater pump and treat systems can remove PFAS however they are not effective at removing large amounts of contaminant mass and they are also very costly since these systems tend to operate over long periods of time, typically decades. Some success has been reported using immobilization where for example PFAS waste is mixed with clay and aluminum hydroxide. Long term success with the technology under in-situ conditions has not been demonstrated. Therefore, there is an urgent need for a method and system capable of treating PFAS contaminated soil and water in situ.